There is a continuing push for transistor devices to perform at increasingly higher voltages. For instance, high-voltage transistors capable of serving as an interface between low-voltage transistors and high-voltage end-use devices, such as automotive components are in high demand. At the same time, however, it is crucial to not increase the manufacturing costs of high-voltage transistors. The use of existing process technologies minimize the cost and complexity of producing high voltage transistors and facilitates the production of high and low voltage transistors (e.g., operating voltage of less than about 5 Volts) in the same integrated circuit (IC).
A drain-extended transistor is one type of high voltage transistor design that can be manufactured without any additional processing steps. A drain-extended transistor, such as a drain-extend metal oxide semiconductor (DEMOS) transistor, incorporates a lightly to moderately doped region around one or both of heavily doped source and drain structures. The lightly to moderately doped region is known as a drain-extended well. Transistor fabrication processes to form a drain-extended well that require the use of an additional mask, dopant implantation and annealing steps are unacceptable.
Typically, the drain-extended well is of a same dopant type as the well of another transistor in a complementary MOS (CMOS) device in the IC. For instance, when the DEMOS transistor is an N-type Metal Oxide Semiconductor (NMOS) transistor, it may be associated with a P-type Metal Oxide Semiconductor (PMOS) transistor. Both the drain-extended well of the NMOS transistor and the well of the PMOS transistor are doped with the same dose of n-type dopant, at the same stage in the manufacturing process. A DEMOS transistor fabricated in this fashion can have breakdown voltages up to about 20-25 Volts. Despite their improved performance, however, drain-extended transistors are still susceptible to breakdown at high voltages.
Accordingly, what is needed in the art is a drain-extended transistor having reduced susceptibility to high voltage breakdown and a method of manufacturing the transistor without adding additional steps to existing processes.